reproducible: add link to db schema, thanks for bmwiedemann for pointing out that was missing

Signed-off-by: Holger Levsen <holger@layer-acht.org>

README

@@ -133,7 +133,7 @@ Installation tests inside chroot environments.
 
 * See https://wiki.debian.org/ReproducibleBuilds to learn more about "Reproducible Builds" in Debian and beyond.
 
-* Several jobs are being used to assemble the website https://tests.reproducible-builds.org which is actually a collection of static html and log files (and very few images) being served from this host. Besides the logfiles data is stored in a database which can be downloaded from https://tests.reproducible-builds.org/reproducible.sql.xz. (That copy is updated daily.)
+* Several jobs are being used to assemble the website https://tests.reproducible-builds.org which is actually a collection of static html and log files (and very few images) being served from this host. Besides the logfiles data is stored in a database (schema description at https://tests.reproducible-builds.org/reproducibledb.html) which can be downloaded from https://tests.reproducible-builds.org/reproducible.sql.xz. (That copy is updated daily.)
 
 * The (current) purpose of https://tests.reproducible-builds.org is to show the potential of reproducible builds for Debian - and six other projects currently. This is research, showing what could (and should) be done... check https://wiki.debian.org/ReproducibleBuilds for the real status of the project for Debian!